CCR2 in Hematopoietic Stem Cell Homing, Macrophage Polarization and Organ Repair

描述(申请人提供)：造血干细胞(HSCs)和祖细胞(HPC)是骨髓来源的细胞，可产生终末分化的循环血细胞。最近的研究表明，这些细胞参与了炎症背景下实质组织的修复，但调节这种运输的信号知之甚少。在NIH资助的其他工作中，我们发现并克隆了CCR2，这是一种趋化因子受体，调节单核细胞向MCP-1的迁移，并表明CCR2-/-小鼠在动脉粥样硬化的小鼠模型中受到保护。在未发表的初步结果中，我们现在发现CCR2表达在原始HSC的亚群上以及一些髓系HPC上。CCR2介导c-Kit林骨髓来源细胞对MCP-1和MCP-3的趋化作用。在注射硫代乙醇酸盐后，WT，而不是CCR2-/-干细胞被活跃地招募到腹膜，并在注射对乙酰氨基酚后被招募到肝脏。值得注意的是，输注CCR2/，而不是CCR2-/-HSCs/HPC加速了肝损伤的缓解，并且招募的细胞表达了M2巨噬细胞表型的特征基因。基于这些最新发现，我们提出了三个相互关联的具体目标，以确定CCR2在HSC/HPC贩运中的作用，以及它们在解决炎症和损伤方面的潜在作用。在特定的目标1中，我们将量化CCR2在早期造血干细胞上的表达。我们将验证CCR2在真实的、自我复制的干细胞上表达的假设，并介导它们对组织炎症和损伤部位的趋化作用。利用新型CCR2/RFP敲入小鼠，我们将定量检测CCR2在小鼠造血树所有分支的HSCs/HPC上的表达，并确定CCR2的激活是否动员骨髓中的HSCs和HPC。在特定的目标2中，我们将确定CCR2介导的HSC或HPC的募集是否有助于急性(扑热息痛)和慢性(四氯化碳)诱导的肝毒性模型中炎症和缺血性损伤的解决，将决定被招募的干细胞和祖细胞的命运，并将检验这样的假设，即为那些表达CCR2的HSCs/HPC富集会显著增强组织修复。在具体目标3中，我们将把注意力转向实验性心肌梗死小鼠的模型，并将确定CCR2或CCR2-HSCs/HPC是否加速心功能的恢复，以及CCR2拮抗剂是否减轻炎症并促进功能恢复。上述工作的完成将确定调控骨髓干细胞和祖细胞归巢到损伤组织的信号，并进一步从机制上理解它们在组织修复和再生中的作用。

DESCRIPTION (provided by applicant): Hematopoietic stem cells (HSCs) and progenitors (HPCs) are bone-marrow derived cells that give rise to terminally differentiated circulating blood cells. Recent work has implicated these cells in the repair of parenchymal tissue in the setting of inflammation, but the signals that regulate this trafficking are poorly understood. In other NIH funded worked we discovered and cloned CCR2, the chemokine receptor that regulates monocyte migration to MCP-1, and showed that CCR2-/- mice are protected in murine models of atherosclerosis. In preliminary, unpublished results we have now found that CCR2 is expressed on subsets of primitive HSCs as well as some myeloid HPCs. CCR2 mediates the chemotaxis of c-Kit+Lin- bone marrow derived cells to MCP-1 and MCP-3. Following instillation of thioglycollate WT, but not CCR2-/- stem cells were actively recruited to the peritoneum, and to the liver following administration of acetaminophen. Significantly, infusion of CCR2+/+, but not CCR2-/- HSCs/HPCs accelerated the resolution of liver damage, and the recruited cells expressed genes characteristic of the M2 macrophage phenotype. Building on these recent findings, we propose three interrelated specific aims to define the role of CCR2 in HSC/HPC trafficking, and their potential roles in the resolution of inflammation and injury. In Specific Aim 1 we will quantify expression of CCR2 on early hematopoietic stem cells. We will test the hypothesis that CCR2 is expressed on true, self-replicating stem cells, and mediates their chemotaxis to sites of tissue inflammation and injury. Using novel CCR2/RFP knock-in mice, we will quantify the expression of CCR2 on HSCs/HPCs in all branches of the hematopoietic tree in mice and determine whether activation of CCR2 mobilizes HSCs and HPCs from bone marrow. In Specific Aim 2 we will determine whether CCR2-mediated recruitment of HSCs or HPCs contributes to the resolution of inflammation and ischemic injury in models of acute (acetaminophen)- and chronic (carbon tetrachloride)-induced hepatotoxicity, will determine the fate of the recruited stem and progenitor cells, and will test the hypothesis that enriching HSCs/HPCs for those that express CCR2 will significanlty enhances tissue repair. In Specific Aim 3 we will turn our attention to a model of experimental myocardial infraction in mice, and will determine if CCR2+ or CCR2- HSCs/HPCs accelerate recovery of cardiac function, and whether CCR2 antagonists reduce inflammation and enhance functional recovery. Completion of the work described above will identify the signals regulating the homing of bone marrow stem and progenitor cells to injured tissue, and further our mechanistic understanding of their role in tissue repair and regeneration.